A simple technique for assessing the cuticular diffusion of humic acid biostimulants

Abstract

Background Experimental determination of the extent and rate of transport of liquid humates supplied to plants is critical in testing physiological effects of such biostimulants which are often supplied as foliar sprays. Therefore, an original experimental method for the qualitative investigation and quantitative description of the penetration of humates through plant cuticles is proposed, tested, and evaluated. Results The proposed method involves the isolation of model plant leaf cuticles and the subsequent in vitro evaluation of cuticular humate transport. The employed novel methodology is based on a simple diffusion couple arrangement involving continuous spectrophotometric determination of the amount of penetrated humate in a hydrogel diffusion medium. Prunus laurocerasus leaf cuticles were isolated by chemical and enzymatic treatment and the rate of cuticular penetration of a commercial humate (lignohumate) was estimated over time in quantitative and qualitative terms. Different rates of lignohumate transport were determined for abaxial and adaxial leaf cuticles also in relation to the different cuticular extraction methods tested. Conclusions The proposed methodology represents a simple and cheap experimental tool for the study on the trans-cuticular penetration of humic-based biostimulants.

From Lab to Field: Role of Humic Substances Under Open-Field and Greenhouse Conditions as Biostimulant and Biocontrol Agent

“…Since the 1940s and 1950s, scientific research on the beneficial impact of foliar application has been explored (Tanou et al, 2017). There exist two theories to explain how exogenous inputs via foliar application are delivered to plant cell tissue, once they reached leaf surface: (1) transfer into leaf tissues via transcuticular penetration (Smilkova et al, 2019); or (2) penetration through leaf stomata (Tejada et al, 2016). Many authors report that micronutrient contents are increased by HS rather than macronutrient in field level (Fernández-Escobar et al, 1996;Çelik et al, 2011;Fatma et al, 2015;Balmori et al, 2019).…”

How the Supramolecular Nature of Lignohumate Affects Its Diffusion in Agarose Hydrogel

“…As mentioned above, the lignohumate is frequently used in agricultural and horticultural applications. Nowadays, foliar applications of fertilizers and bio-stimulants complement standard root fertilization [ 8 , 43 ]. Diffusion processes play an important role in both methods of fertilization because the application of fertilizers is connected with the penetration into plant organs such as leaves and roots.…”

“…Lignohumate is an industrially produced analog of natural humic substances, produced by thermal processing of technical lignosulfonate, which is based on the oxidation and hydrolytic destruction of lignin-containing raw material [ 1 , 2 ]. It can promote plant growth and therefore it is widely used for agricultural and horticultural purposes [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. It was found that its application can reduce leaching of nitrogen into the soil solution [ 2 ], reduce the toxic effect of pesticides, improve the nitrogen balance of soils, increase the basal respiration of the soil, and has a positive effect on soil biological activity [ 9 ].…”

“…Present studies of lignohumate are focused mainly on its agricultural and horticultural applications [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ]; therefore, studies dealing with its structural characterization and other properties are relatively scarce. Some works [ 2 , 24 ] used chemical (elemental analysis) and spectral (UV/VIS, FT-IR nad 13 C-NMR) methods for the characterization of lignohumate and its comparison with humic material extracted from different natural matrices.…”

“…Some works [ 2 , 24 ] used chemical (elemental analysis) and spectral (UV/VIS, FT-IR nad 13 C-NMR) methods for the characterization of lignohumate and its comparison with humic material extracted from different natural matrices. The diffusion of lignohumate through plant cuticles was studied in our previous work [ 8 ]. The cuticle was placed between two cuvettes filled by agarose hydrogels.…”